The purpose of this work is to examine the dynamic properties of macromolecules and macromolecular aggregates, using temperature-jump relaxation kinetics and magnetic resonance spectroscopy. The mechanism of thermal unfolding of RNA molecules will be studied by these methods, yielding information on the nature of the secondary structure, the existence of tertiary structure and the mechanism of structural changes. Point mutants tRNA and tRNA precursors will be studied to detrmine the kinetic, thermodynamic and structural consequences of single base changes. The dynamic properties of ribosomes under perturbation by temperature and/or electric fields will be examined to determine the rate of ribosomal subunit recombination and the rate of first order structural changes in the particles. The rate of binding intercalating ligands to closed circular DNA will be studied to determine the viscous resistance to winding and unwinding the superhelix.